diyAudio - rjm
Go Back   Home > Forums > Blogs

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Old

Audio op amp comparison NE5534A vs. OPA134

Posted 10th February 2012 at 10:49 PM by rjm
Updated 11th February 2012 at 02:48 AM by rjm

Finally got around to some more comparison listening with the Sapphire headphone amplifier. To recap: the circuit has an open loop diamond buffer output, so the op amp is just providing voltage gain. It configured for a non-inverting gain of 21 dB to match my 300 ohm HD600 headphones. Pretty much textbook operating conditions.

The op amp inputs are impedance balanced at about 1 kohm. This is about the crossover point where you start thinking about using FET input stages, but BJTs should still be fine.

I'm interested to see if there is a definite signature to a FET-input opamp. The original build called for an OPA134, which is a JFET input circuit. I tried the OPA27, which is a low-noise, high-input-current BJT design, and last night I tried the NE5534A, a classic general purpose audio opamp with bipolar inputs.

I've long been in agreement with Douglas Self on the NE5532/NE5534 : anyone who reports these op amps sound bad is either not using...
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 4213 Comments 1 rjm is offline
Old

RJM Z-reg + Pass B1

Posted 3rd February 2012 at 11:53 PM by rjm
Updated 4th February 2012 at 12:01 AM by rjm

I was asked to suggest a voltage regulator for the First Watt (Pass DIY) B1 buffer. One thing led to another and the next thing I'd sketched up a circuit board for the buffer as well as the regulator.

It's like a B-board, but with the JFET buffer instead of the diamond buffer, and with a single supply and, hence, the coupling caps front and back. Since it's using JFETs for the buffer I used a JFET for the pass device in the regulator, too.

Full credit to Nelson Pass for his design.

Eagle files do not show 2SK170 because the package is not in Eagle. All transistors 2SK170 or equivalent. Zener is 18-22V DO35 or DO41 i.e. Vishay BZX85. V++ is 5-15 V above whatever you select the Zener reference to be.
Attached Thumbnails
Click image for larger version

Name:	b1-10c-brd.png
Views:	1775
Size:	19.7 KB
ID:	586   Click image for larger version

Name:	b1-10c-sch.png
Views:	2989
Size:	21.0 KB
ID:	587  
Attached Files
File Type: zip Pass B1 RJM 10c.zip (61.8 KB, 322 views)
rjm's Avatar
rjm
diyAudio Member
Views 2441 Comments 4 rjm is offline
Old

The Z-reg

Posted 1st February 2012 at 10:58 PM by rjm
Updated 2nd April 2012 at 02:02 AM by rjm

This is a followup of sorts to the X-reg, though there is nothing original about the circuit this time around.

It's just a Zener voltage regulator with a series pass transistor. I lifted this particular configuration from the Pionner C-21 preamplifier and re-tuned it for op amp applications. My main interest here is trying to make a small and convenient board layout.

I've used this circuit block already in the Sapphire amp and come away impressed.

The output is about 1 V less than the Zener voltage, and the input voltage should be about 3-6 V above the Zener reference voltage. I'm working here with 17 V unregulated supply and 12 V Zeners, but the values can be reconfigured easily enough for any output from 4-24 V

This is a low current circuit. If you are just powering a few op amps, no heatsinks are needed. Above 25 mA small heatsinks are a good idea. The circuit is not designed for output currents above 100 mA.
Attached Thumbnails
Click image for larger version

Name:	zreg10d-brd.png
Views:	1010
Size:	17.4 KB
ID:	583   Click image for larger version

Name:	zreg10d-sch.png
Views:	671
Size:	20.2 KB
ID:	584  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 713 Comments 0 rjm is offline
Old

Current Feedback Amplifier

Posted 31st January 2012 at 05:15 AM by rjm
Updated 31st January 2012 at 05:22 AM by rjm

Found this today: DC Coupled Amplifiers for Audio from an 11 year old web page by one Knut Harald Nygaard.

I've taken some minor liberties with the circuit, shown in the second, color image below. Replaced the current sources with resistors and moved the output buffer out of the feedback loop.

Note the resultant double symmetry of the dual-diamond buffer topology, highlighted in blue.
Attached Thumbnails
Click image for larger version

Name:	dcff15 original.png
Views:	1599
Size:	7.6 KB
ID:	581   Click image for larger version

Name:	dcff15 rm mod color.png
Views:	1957
Size:	14.6 KB
ID:	582  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 2478 Comments 2 rjm is offline
Old

Whither Next for RJM Audio?

Posted 26th January 2012 at 12:22 AM by rjm
Updated 1st February 2012 at 08:20 AM by rjm

On the occasion of selling the 100th and last VSPS Stereo Kit, it's time to consider what direction(s) RJM Audio will take over the next little while.

A. A minor revision of the stereo VSPS board is planned. Just a point release to address feedback I received over the last couple of years. Point release on current boards (Phonoclone 3, VSPS 300, Sapphire) expected when I deplete existing stock and have to re-order.

B. Since my circuit designs are essentially modular (the voltage regulation of the Sapphire headphone amp could be used with the Phonoclone, the output stage of the Sapphire could be detached and used on the output buffer on the VSPS...) I'm going to work on bringing that vision to a concrete reality by developing "swap-in swap-out" circuit boards... like those toys where you can change out the head, body and legs of a character to make many variations.
  1. X-reg board
  2. Zener reg board
  3. basic op amp gain block board
  4. VSPS and
...
rjm's Avatar
rjm
diyAudio Member
Posted in Uncategorized
Views 1166 Comments 4 rjm is offline
Old

My system (Jan 2012)

Posted 23rd January 2012 at 12:12 PM by rjm
Updated 26th January 2012 at 02:57 AM by rjm

Biggest changeover in many years.

Denon DP-2000, DA-307, DL-103 turntable/tonearm/cartridge
Phonoclone 3 with 160 VA Plitron power supply
47 Labs "Treasure" model 0247 preamplifier
47 Labs "Treasure" model 0347 amplifier
Onkyo D-605SR speakers
Cables by oyaide, mostly.
(photo: Pentax K10D, Pentax FA 31mm F1.8 AL Limited)
Attached Thumbnails
Click image for larger version

Name:	IMGP1552j 1280.jpg
Views:	1126
Size:	369.4 KB
ID:	580  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 1131 Comments 0 rjm is offline
Old

Oh, MY!

Posted 23rd January 2012 at 06:51 AM by rjm

Denon DL-A100

Transparent DL-103 for Denon's 100th anniversary.
Attached Thumbnails
Click image for larger version

Name:	dla100_2.jpg
Views:	203
Size:	10.3 KB
ID:	577  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 808 Comments 2 rjm is offline
Old

op amps for audio

Posted 23rd January 2012 at 06:36 AM by rjm

Douglas Self on op amps for audio, which I read before in slightly different form, on another web site somewhere, many years ago... today was a refresher course.

Excerpts from op amps in small signal audio design, by D. Self [Part 1, part 2, part 3, part 4].

I suppose I should get with the times and start using the LM4562 seeing as it is available in DIP8 now. (I had this memory that it was only SOIC, go figure...) Pity it's dual only. On the other hand, that leads to some neat ideas, like a compact version of the Sapphire amp for example, or the X-reg.

I am struck by how few choices we really have when it comes to practical op amps for audio in single DIP8 packages. There is the NE5534, TL071 and TL051, the OPA134, the OPA604, and OPA27, OPA627. Maybe the AD797 but I have yet to see the point. Given that the TL1071 and derivatives are outdated and replaced essentially by the OPA134, and given the excessive cost (and questionable sonic benefit)...
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 1283 Comments 2 rjm is offline
Old

The new system, up and running.

Posted 22nd January 2012 at 10:52 AM by rjm
Updated 25th January 2012 at 07:57 AM by rjm

So now we have the model 0247 DAC/preamp/headphone amplifier and model 0347 power amplifier in the main system. That's the old Denon DP-2000 TT, Phonoclone 3, and Onkyo D-605SR speakers.

The gain of the 0347 is 30 dB, so with the 0247 doing duty as a preamp the overall gain is a tad high, but it's perfectly useable. I'll look at the passive preamp options (including the model 0447) at a later date.

Anyhow, the big news is it completely destroys the non-inverting LM3875 Gainclone I have been using for the last decade, so badly, in fact, I'm starting to wonder if my Gainclone was busted. In comparison with the 0347 it sounds like a distorted, uncontrolled mess.

Since my speakers are really very modest in quality (though at 82dB and 6 ohms, a bit of a rough load) I wasn't expecting much difference one way the other, so this comes as a severe shock.

Unfortunately I'm not within reach of a good reference system to give the 0347 a real evaluation....
Attached Thumbnails
Click image for larger version

Name:	IMGP1513j 1280.jpg
Views:	738
Size:	348.1 KB
ID:	576  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 1150 Comments 1 rjm is offline
Old

47 Labs Treasure 0347 : trials and tribulations

Posted 20th January 2012 at 11:48 AM by rjm

And not even sure what a tribulation is, but I'm sure I've had at least one building this amp.

Like the 0247 it's not so much difficult as it is painstaking hard work. The output transistors have to be mounted "just so" so the boards screw to the case properly, the wiring of the thermal protection transistors and gluing them to the output devices is tricky and easy to mess up.

I triple-checked and was rewarded by, it seems, error free boards. I messed up and wired the mute switch incorrectly though (the photos show it wrong, in case you come across this blog post looking for help) and I think the switch has a fault somehow as L and R channels appear to me mixed together. Taming the offsets gave me considerable grief but I think its all OK now.

Tomorrow I'll hook it up to the speakers and see what happens.
Attached Thumbnails
Click image for larger version

Name:	DSC_3005 1280.jpg
Views:	1542
Size:	311.5 KB
ID:	569   Click image for larger version

Name:	DSC_2991 1280.jpg
Views:	1951
Size:	401.7 KB
ID:	570   Click image for larger version

Name:	DSC_2969 1280.jpg
Views:	1202
Size:	243.7 KB
ID:	571   Click image for larger version

Name:	DSC_3007 1280.jpg
Views:	2250
Size:	290.9 KB
ID:	572  
Attached Files
rjm's Avatar
rjm
diyAudio Member
Views 2064 Comments 1 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 09:43 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2